The present invention relates to stabilizer compositions for polyvinyl chloride resins and to polyvinyl chloride resin compositions having improved resistance to degradation caused by heat and light. More particularly, the present invention relates to liquid stabilizer compositions comprising at least one methyltin compound and one butyltin compound wherein each compound has mercapto carboxylic acid ester and/or carboxylate moieties. In this regard, the stabilizers of the present invention are characterized by visual homogeneity. In addition, the polyvinyl chloride resin compositions incorporating these stabilizers exhibit a favorable balance of the critical parameters of initial color control, processing heat stability, and long term resistance to change in color and mechanical properties when exposed to light and ultraviolet, i.e. light stability.
As is well known to those skilled-in-the-art, various halogen-containing polymers, particularly vinyl halide polymers that include homopolymers of vinyl chloride and copolymers of vinyl chloride with other monomers, may degrade when subjected to heat or light for an extended period as manifested by darkening of the resin and by an increase in brittleness. These defects may render the resin unsuitable for many uses because the darkening produces an unsightly appearance, and the increased brittleness may cause mechanical failures. A wide variety of materials has heretofore been proposed to stabilize halogen-containing polymers.
For instance, the use of organotin mercapto carboxylic acid esters as stabilizers for polyvinyl chloride resins is well known, and is generally set forth in such early patents as U.S. Pat. Nos. 2,753,825 to Leistner et al., issued Jun. 26, 1956, 2,641,596 to Leistner et al., issued Jun. 9, 1953, and 2,648,650 to Weinberg et al., issued Aug. 11, 1953. These organotin compounds have in common a hydrocarbon group directly attached to the tin atom through a carbon atom, and a sulfur-containing radical attached to the tin atom through the sulfur atom.
This type of organotin stabilizer is recognized as being among the most effective stabilizers for inhibiting the degradation of polyvinyl chloride resins at the high temperatures, e.g. 350.degree. F. to 400.degree. F., to which they are subjected during processing. Resins stabilized only with these organotin mercapto carboxylic acid esters, however, do not exhibit the degree of light stability often desired for applications such as siding, and window and door profiles wherein resistance to change in color and mechanical properties when exposed to light and ultraviolet is an important factor.
Several types of sulfur-free organotin compounds have been suggested in which a hydrocarbon group is directly attached to tin through a carbon atom, and an oxygen-containing group, such as an ester group, is attached to tin through oxygen. This type of stabilizer is also well known and is generally set forth in numerous patents including U.S. Pat. No. 2,344,002 to Rugeley et al., issued Mar. 14, 1944. Organotin compounds of this type, such as dibutyltin dilaurate, are excellent light stabilizers but are relatively poor heat stabilizers at the high temperatures, such as 350.degree. F. to 400.degree. F., commonly used today to process polyvinyl chloride compositions for siding, and window and door profiles.
A number of organotin stabilizers have been proposed that include a mercapto carboxylic acid ester moiety as well as a carboxylate moiety in a single compound or in a combination of two or more compounds. For example, U.S. Pat. No. 2,914,506 to Mack et al. discloses compounds broadly defined by the formula R R' Sn (SX) (Z) wherein R and R' may be the same or different monovalent hydrocarbon radicals, SX may be, among other things, an ester of a mercapto acid, and Z may be, among other things, a carboxylic acid linked through the oxygen of the carboxylic acid group to the tin atom.
United Kingdom Patent No. 1,008,845 to Smith, discloses a multicomponent stabilizer for ethylenically unsaturated monomers including chlorine-containing monomers. These multicomponent stabilizers include at least three different types of organotin compounds with a variety of other additives. Included within the three types of organotin compounds are diorganotin mercapto acid esters and diorganotin carboxylates.
According to U.S. Pat. No. 3,562,305 to Hoch, the incorporation into an organotin mercapto acid ester of a small amount of organotin carboxylate yields products having a substantially reduced tendency to decompose on standing and are at least as effective as the untreated organotin mercapto acid esters as stabilizers for vinyl halide resin compositions.
United Kingdom Patent No. 1,251,864 to M&T International N.V., discloses compositions for stabilizing halogen-containing resins against the deteriorative effects of heat which compositions can comprise an organotin mercapto acid ester, such as dibutyltin bis (iso-octyl) mercaptoacetate, and an organotin carboxylate such as butyltin tris (laurate). Additionally, U.S. Pat. No. 4,698,368 to Muller, discloses a stabilizer composition that can include an organotin mercaptopropionate and an organotin carboxylate.
These patents as well as others, such as U.S. Pat. No. 3,810,868 to Weisfeld et al., provide sufficient information to those skilled-in-the-art to produce these organotin mercapto acid esters and organotin carboxylates.
It is also well known to those skilled-in-the-art to incorporate additives such as phenolic antioxidants in the organotin stabilizer compositions for enhanced performance. The art is replete with examples of such additives such as those disclosed in U.S. Pat. Nos. 3,398,114 to Pollock, 3,424,717 to Gottlieb et al. and 4,418,169 to Gibbons et al.
Many of these stabilizers and additives have achieved some measure of success at stabilizing halogen-containing resins against the degradative action of heat and light, but there are many applications in which a greater degree of heat and light stability is desired than has heretofore been readily attainable. Additionally, not all of these stabilizers are homogeneous liquids at room temperatures. Such homogenity is a characteristic often desired by end users for handling and processing ease. Those skilled-in-the-art recognize that although certain organotin stabilizers exhibit different heat and light stability properties there is no definitive predictive rule for providing a stabilizer composition that has all the features of liquid homogeneity, initial color control, processing heat stability, light stability, and overall processability.
For example, U.S. Pat. No. 4,418,169 to Gibbons et al., notes it has been suggested that the dialkyltin diesters such as dibutyltin dilaurate and dibutyltin maleate, which are highly effective in preventing the light-induced degradation of polymers, be combined with a secondary or auxiliary heat stabilizer to improve their ability to protect the vinyl chloride polymers against heat degradation. According to the '169 patent, typical of such auxiliary heat stabilizers are the alkylated methylene bisphenols, which may be capable of increasing the heat stability of polymer compositions somewhat but which may also have a pronounced deleterious effect upon light stability. In this regard, the '169 patent states it is not uncommon for such auxiliary heat stabilizers to reduce the light stability of the polymer composition to as little as 20% of that which may be obtained in the absence of such a stabilizer.
Accordingly, a general object of the present invention is to provide an improved stabilizer composition.
It is another object of the present invention to provide a stabilizer composition that is a homogeneous liquid at room temperature.
It is another object of the present invention to provide a method of stabilizing halogen-containing organic polymer or resin compositions, particularly vinyl halide polymers, against heat and light degradation.
It is a further object of the present invention to provide novel stabilized halogen-containing polymers.
These and other objects of the present invention will be apparent to those skilled-in-the-art from the following description.